The aquatint is a technique of indirect engraving of metal (copper or zinc) which consists in enriching a matrix (printing ) of light and dark tones . It is complementary etching. Sprinkle the sheet of powder of bitumen or rosin , it is warmed slightly so that it adheres by fusion so that at the time dell'acidatura are corroded only the spaces between the grains of powder , producing a rough surface ( granite type ) that will retain the ink depending on the type of etching that has been made . Awarded graining will draw negative. The parts you want to go white coated paint . With aquatint you can do, even in the same matrix , using different characteristics of grain powders of different thickness and with repeated etching.